Method of manufacturing surface emitting laser, and surface emitting laser, surface emitting laser array, optical scanning device and image forming apparatus

ABSTRACT

A disclosed method of manufacturing a surface emitting laser includes laminating a transparent dielectric layer on an upper surface of a laminated body; forming a first resist pattern on an upper surface of the dielectric layer, the first resist pattern including a pattern defining an outer perimeter of a mesa structure and a pattern protecting a region corresponding to one of the relatively high reflection rate part and the relatively low reflection rate part included in an emitting region; etching the dielectric layer by using the first resist pattern as an etching mask; and forming a second resist pattern protecting a region corresponding to an entire emitting region. These steps are performed before the mesa structure is formed.

TECHNICAL FIELD

The present invention relates to a surface emitting laser, a surfaceemitting laser array, an optical scanning device, an image formingapparatus, and a method of manufacturing a surface emitting laser. Morespecifically, the present invention relates to a method of manufacturinga surface emitting laser capable of emitting light in the directionorthogonal to its substrate; a surface emitting laser and a surfaceemitting laser array capable of emitting light in the directionorthogonal to their substrate; an optical scanning device having thesurface emitting laser or the surface emitting laser array; and an imageforming apparatus having the optical scanning device.

BACKGROUND ART

A Vertical Cavity Surface Emitting Laser (hereinafter may be referred toas “VCSEL”) is a semiconductor laser capable of emitting light in thedirection orthogonal to its substrate. When compared with edge emittingsemiconductor lasers capable of emitting light in the direction parallelto its substrate, the VCSEL may have some advantages such as lower cost,lower energy consumption, smaller size, and being appropriatelyapplicable to two-dimensionally integrated devices. Recently, because ofthose advantages, the VCSEL has attracted increased attention.

The surface emitting laser has a current confined structure to enhancecurrent influx efficiency. To form the current confined structure, aselective oxidation process is usually performed on an AlAs (Al:aluminum, As: arsenic) layer. In the following, the current confinedstructure may also be referred to as an “oxide-confined structure” forconvenience (see, for example, Patent Document 1). The oxide-confinedstructure may be formed by forming a mesa structure having predeterminedsizes and having a side surface where a selectively-oxidized layer isexposed. Then, the formed mesa structure is processed under awater-vapor atmosphere so that aluminum (Al) in the selectively-oxidizedlayer is selectively oxidized from the side surface of the mesastructure. By doing this, an unoxidized region remains in the centerportion of the mesa structure. The unoxidized region (hereinafterreferred to as a “confined region” for explanatory purposes) becomes apassing region (or a “current passage region”) through which a drivingcurrent of the surface emitting laser passes. As described above, thecurrent may be easily contained. The refractive index of thealuminum-oxidized layer (Al_(x)O_(y)) (hereinafter simplified as an“oxidized layer”) in the oxide-confined structure is approximately 1.6,which is lower than that of semiconductor layers. Because of thisfeature, a refractive index difference is generated in the lateraldirection in a resonator structure of the surface emitting laser, andthe light is confined in the center of the mesa structure, therebyimproving the emission efficiency of the surface emitting laser. As aresult, it becomes possible to obtain excellent characteristics such aslower threshold current and higher efficiency.

The surface emitting laser may be generally applied to a light source ofan optical writing system in a printer (oscillation wavelength: 780 nmband), a light source of an optical writing system in an optical diskdevice (oscillation wavelength: 780 nm band and 850 nm band), and alight source of an optical transmission system such as LAN (Local AreaNetwork) using optical fibers (oscillation wavelength: 1.3 μm band and1.5 μm band). Further, the surface emitting laser is also expected to beused as a light source for optical transmission between boards, within aboard, and between chips and within a chip in a Large Scale Integratedcircuit (LSI).

In those application fields, it is generally required that across-sectional shape of the light emitted from the surface emittinglaser (hereinafter referred to as “emitting light”) be circular. Toachieve the circular cross-sectional shape, it is required to controlhigher-order transverse-mode oscillation.

To that end, for example, Patent Document 2 discloses a method ofcontrolling the transverse-mode oscillation by forming an opticallytransparent film on an emitting surface and differentiating thereflection rates between the center part and its peripheral part of theemitting region.

SUMMARY OF THE INVENTION Means for Solving the Problems

The inventors of the present invention have conducted extensive researchon this technical field and have obtained a new knowledge that, when anoptically transparent film(s) (hereinafter simplified as an “opticalfilter(s)”) is formed on an emitting surface of a laser light (asexemplarily shown in FIGS. 23(A) and 23(B) in), a light emitting angle(indicated in FIG. 23(A)) is influenced by the relative positionalrelationship between the current passage region and the optical filters.In the figures, an XYZ three-dimensional orthogonal coordinate system isemployed, assuming that the Z axis direction is a direction orthogonalto the surface of the substrate. Further, there are two optical filterswhich face each other and are separated in the x direction.

Further, the “light emitting angle” refers to an inclined angle betweenthe direction orthogonal to surface of the substrate (in this case, Zaxis direction) and the direction along which the emitted lightintensity is maximized. Herein, a clockwise inclined direction withrespect to the direction orthogonal to the surface of the substrate isindicated by a plus sign (+), and on the other hand, a counterclockwiseinclined direction with respect to the direction orthogonal to thesurface of the substrate is indicated by a minus sign (−).

Further, FIGS. 24 and 25 illustrate a relationship between a positionaldisplacement amount of the centroid of the two optical filters withrespect to the center of the current passage region when viewed from adirection orthogonal to the surface of the substrate (hereinaftersimplified as “displacement amount”) and the light emitting angle.

More specifically, FIG. 24 shows results of experiments conducted tomeasure the light emitting angle while changing the centroid of the twooptical filters with respect to the center of the current passage regionin the Y axis direction. In this case, it is assumed that when thedirection of the displacement amount is in the +Y direction, thedisplacement amount is indicated by the plus sign (+); on the otherhand, when the direction of the displacement amount is in the −Ydirection, the displacement amount is indicated by the minus sign (−).As the results of the experiments, the light emitting angle in the Xaxis direction is substantially constant and is substantially the sameas 0 degrees. when the displacement amount changes in the Y axisdirection. On the other hand, the magnitude (absolute value) of thelight emitting angle in the Y axis direction is likely to increase asthe magnitude (absolute value) of the displacement amount in the Y axisdirection increases.

On the other hand, FIG. 25 shows results of experiments conducted tomeasure the light emitting angle while changing the centroid of the twooptical filters with respect to the center of the current passage regionin the X axis direction. In this case, it is assumed that when thedirection of the displacement amount is in the +X direction, thedisplacement amount is indicated by the plus sign (+); on the otherhand, when the direction of the displacement amount is in the −Xdirection, the displacement amount is indicated by the minus sign (−).As the results of the experiments, the light emitting angle in the Yaxis direction is substantially constant and is substantially the sameas 0 degrees. when the displacement amount changes in the X axisdirection. On the other hand, the magnitude (absolute value) of thelight emitting angle in the X axis direction is likely to increase asthe magnitude (absolute value) of the displacement amount in the X axisdirection increases.

To obtain high-resolution images in an image forming apparatus, it maybe important to form a minute circular light spot at a desired positionon a to-be-scanned surface. Further, to form the minute circular lightspot at the desired position on the to-be-scanned surface, according toresults of various experiments and theoretical calculations, it may benecessary to control the magnitude (absolute value) of the lightemitting angle in all the directions to be equal to or less than 0.2degrees.

To that end, according to the relationship illustrated in FIGS. 24 and25 or the like, it is necessary to control (reduce) the magnitude(absolute value) of the displacement amount in the surface emittinglaser to be equal to or less than 0.1 μm.

However, when the method disclosed in Patent Document 1 is employed, itis difficult to stably manufacture the surface emitting lasers havingthe magnitude (absolute value) of the displacement amount equal to orless than 0.1 μm.

The present invention is made based on the above-described new knowledgeobtained by the inventers of the present invention, and has thefollowing configurations.

According to a first aspect of the present invention, there is provideda method of manufacturing a surface emitting laser. The surface emittinglaser includes a laminated body in which a lower reflection mirror, aresonance structure, and an upper reflection mirror are laminated on asubstrate, the resonance structure including an active layer, the upperreflection mirror including a selectively-oxidized layer, and a mesastructure formed in the laminated body and capable of serving as anemitting section, the emitting section including a current confinedstructure and an emitting region, the current confined structureincluding an oxide surrounding a current passage region, the emittingregion including a relatively high reflection rate part and a relativelylow reflection rate part. The method of manufacturing a surface emittinglaser according to this aspect of the present invention includes a firstdielectric layer laminating step of laminating a transparent dielectriclayer on an upper surface of the laminated body; a first resist patternforming step of forming a first resist pattern on an upper surface ofthe dielectric layer, the first resist pattern including a patterndefining an outer perimeter of the mesa structure and a patternprotecting a region corresponding to one of the relatively highreflection rate part and the relatively low reflection rate partincluded in the emitting region; a dielectric layer etching step ofetching the dielectric layer by using the first resist pattern as anetching mask; and a second resist pattern forming step of forming asecond resist pattern protecting a region corresponding to an entireemitting region. Further, in this case, the first dielectric layerlaminating step, the first resist pattern forming step, the dielectriclayer etching step, and the second resist pattern forming step areperformed before the mesa structure is formed.

By having this configuration, it may become possible to stablymanufacture the surface emitting lasers having the magnitude (absolutevalue) of the displacement amount equal to or less than 0.1 μm whilebetter controlling the transverse-mode oscillation.

According to a second aspect of the present invention, there is provideda surface emitting laser including an emitting section having a mesastructure in which a lower reflection mirror, a resonance structure, andan upper reflection mirror are laminated on a substrate, the resonancestructure including an active layer, the upper reflection mirrorincluding a current confined structure including an oxide surrounding acurrent passage region, the emitting section including an emittingregion, an entire surface of the emitting region being covered with atransparent dielectric, the emitting region including a relatively highreflection rate part and a relatively low reflection rate part. Further,in the surface emitting laser, when viewed from a direction orthogonalto the substrate after removing an electrode surrounding the emittingregion, an outer perimeter of the mesa structure is formed ofdielectric, and the thickness of the dielectric is the same as that of apart having two layers of the dielectric in the emitting region.

By having this configuration, it may become possible to control themagnitude (absolute value) of the light emitting angle to be equal to orless than 0.2 degrees. while better controlling the transverse-modeoscillation without incurring high cost.

According to a third aspect of the present invention, there is provideda surface emitting laser array including integrated surface emittinglasers according to the second aspect of the present invention.

In the surface emitting laser array, the surface emitting lasersaccording to the second aspect of the present invention are integrated.Therefore, in each emitting section, it may become possible to control(reduce) the magnitude (absolute value) of the light emitting angle tobe equal to or less than 0.2 degrees. while better controlling thetransverse-mode oscillation.

According to a fourth aspect of the present invention, there is providedan optical scanning device capable of scanning a to-be-scanned surfaceby a light. The optical scanning device includes a light source having asurface emitting laser according to the second aspect of the presentinvention, a deflector deflecting a light from the light source, and ascanning optical system focusing the light deflected by the deflectoronto the to-be-scanned surface.

In this optical scanning device, the light sources including the surfaceemitting lasers according to the second aspect of the present inventionare integrated. Therefore, in each emitting section, it may becomepossible to perform highly accurate optical scanning without incurringhigh cost.

According to a fifth aspect of the present invention, there is providedan optical scanning device capable of scanning a to-be-scanned surfaceby a light. The optical scanning device includes a light source having asurface emitting laser array according to the third aspect of thepresent invention, a deflector deflecting a light from the light source,and a scanning optical system focusing the light deflected by thedeflector onto the to-be-scanned surface.

In this optical scanning device, the light sources including the surfaceemitting laser array according to the third aspect of the presentinvention are integrated. Therefore, in each emitting section, it maybecome possible to perform highly accurate optical scanning withoutincurring high cost.

According to a sixth aspect of the present invention, there is providedan image forming apparatus including an image carrier and an opticalscanning device according the fourth or the fifth aspect of the presentinvention scanning a light on the image carrier, the light beingmodulated based on image information.

By having this configuration, the image forming apparatus includes anoptical scanning device according the fourth or the fifth aspect of thepresent invention. As a result, it may become possible to form ahigh-quality image without incurring high cost.

Patent Document 1: U.S. Pat. No. 5,493,577

Patent Document 2: Japanese Patent No. 3566902

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing a configuration of a laser printeraccording to an embodiment of the present invention;

FIG. 2 is a schematic drawing showing a configuration of an opticalscanning device in FIG. 1;

FIG. 3 is a drawing showing a configuration of a surface emitting laserincluded in a light source of FIG. 2;

FIGS. 4(A) and 4(B) are drawings showing a substrate of the surfaceemitting laser;

FIG. 5 is an enlarged drawing showing an active layer;

FIGS. 6(A) through 6(C) are drawings (1) showing a method ofmanufacturing the surface emitting laser according to an embodiment ofthe present invention;

FIG. 7 is a drawing showing resist patterns 120 a and 120 b;

FIGS. 8(A) and 8(B) are drawings (2) showing the method of manufacturingthe surface emitting laser according to the embodiment of the presentinvention;

FIG. 9 is a drawing showing a second resist pattern;

FIG. 10 is a cross-sectional view along line A-A′ of FIG. 9;

FIGS. 11(A) through 11(C) are drawings (3) showing the method ofmanufacturing the surface emitting laser according to the embodiment ofthe present invention;

FIGS. 12(A) through 12(D) are drawings (4) showing the method ofmanufacturing the surface emitting laser according to the embodiment ofthe present invention;

FIG. 13 is a partially enlarged drawing (1) showing a mesa structure inFIG. 12(D);

FIG. 14 is a partially enlarged drawing (2) showing the mesa structurein FIG. 12(D);

FIG. 15 is a drawing showing a modified method of manufacturing thesurface emitting laser according to an embodiment of the presentinvention;

FIG. 16 is a vertical cross-sectional view of the surface emitting laserof FIG. 15;

FIGS. 17(A) through 17(G) are drawings (1) showing modifiedconfigurations of a high reflection rate region 122 and a low reflectionrate region 121;

FIGS. 18(A) through 18(C) are drawings (2) showing modifiedconfigurations of the high reflection rate region 122 and the lowreflection rate region 121;

FIG. 19 is a drawing showing a change of a cross-sectional shape of theresist pattern 120 a as a result of baking;

FIG. 20 is a drawing showing a surface emitting laser array;

FIG. 21 is a cross-sectional view along line A-A′ of FIG. 20;

FIG. 22 is a schematic drawing showing a configuration of a colorprinter;

FIG. 23(A) is a drawing illustrating a light emitting angle and opticalfilters;

FIG. 23(B) is a drawing illustrating the optical filters;

FIG. 24 is a graph illustrating a relationship between a displacementamount of the optical filters in Y axis direction and the light emittingangle; and

FIG. 25 is a graph illustrating a relationship between a displacementamount of the optical filters in X axis direction and the light emittingangle.

DESCRIPTION OF THE REFERENCE NUMERALS

11 a: DEFLECTOR-SIDE SCANNING LENS (PART OF SCANNING OPTICAL SYSTEM)

11 b: IMAGE-SURFACE-SIDE SCANNING LENS (PART OF SCANNING OPTICAL SYSTEM)

13: POLYGON MIRROR (DEFLECTOR)

14: LIGHT SOURCE

100: SURFACE EMITTING LASER

101: SUBSTRATE

103: LOWER SEMICONDUCTOR DBR (LOWER REFLECTION MIRROR)

104: LOWER SPACER LAYER (PART OF RESONATOR STRUCTURE)

105: ACTIVE LAYER

106: UPPER SPACER LAYER (PART OF RESONATOR STRUCTURE)

107: UPPER SEMICONDUCTOR DBR (UPPER REFLECTION MIRROR)

108: SELECTIVELY-OXIDIZED LAYER

108 a: OXIDE

108 b: CURRENT PASSAGE REGION

111 a: DIELECTRIC LAYER

111 b: DIELECTRIC LAYER

120 a: RESIST PATTERN (PART OF FIRST RESIST PATTERN)

120 b: RESIST PATTERN (PART OF FIRST RESIST PATTERN)

120 c: RESIST PATTERN (PART OF FIRST RESIST PATTERN)

123: SECOND RESIST PATTERN

125: EMITTING REGION

200: SURFACE EMITTING LASER ARRAY

1000: LASER PRINTER (IMAGE FORMING APPARATUS)

1010: OPTICAL SCANNING DEVICE

1030: PHOTOCONDUCTIVE DRUM (IMAGE CARRIER)

2000: COLOR PRINTER (IMAGE FORMING APPARATUS)

2010: OPTICAL SCANNING DEVICE

K1, C1, M1, AND Y1: PHOTOCONDUCTIVE DRUM (IMAGE CARRIER)

MODE FOR CARRYING OUT THE INVENTION

In the following, an embodiment of the present invention is describedwith reference to FIGS. 1 through 14. FIG. 1 schematically shows aconfiguration of a laser printer 1000 as an image forming apparatusaccording to an embodiment of the present invention.

As shown in FIG. 1, the laser printer 1000 includes an optical scanningdevice 1010, a photoconductive drum 1030, a charger 1031, a developingroller 1032, a transfer charger 1033, a neutralization unit 1034, acleaning unit 1035, a toner cartridge 1036, a feeding roller 1037, afeeding tray 1038, a resist roller pair 1039, a fixing roller 1041, adischarge roller 1042, a discharge tray 1043, a communication controldevice 1050, and a printer control device 1060 collectively controllingthe above parts. Those elements are contained at their predeterminedpositions in a printer chassis 1044.

The communication control device 1050 controls bi-directionalcommunications with a higher-level apparatus (such as a PC) via anetwork.

The photoconductive drum 1030 is a cylindrical member having aphotoconductive layer formed on its surface. Namely, the surface of thephotoconductive drum 1030 is a to-be-scanned surface. Further, thephotoconductive drum 1030 rotates in the arrow direction shown in FIG.1.

The charger 1031, the developing roller 1032, the transfer charger 1033,the neutralization unit 1034, and the cleaning unit 1035 are disposednear the surface of the photoconductive drum 1030. Further, along therotating direction of the photoconductive drum 1030, those elements aredisposed in order of “charger 1031→developing roller 1032→transfercharger 1033→neutralization unit 1034→cleaning unit 1035”.

The charger 1031 uniformly charges the surface of the photoconductivedrum 1030.

The optical scanning device 1010 scans a light flux modulated based onimage information from the higher-level apparatus onto the surface ofthe photoconductive drum 1030, the surface having been charged by thecharger 1031, so that a latent image corresponding to the imageinformation is formed on the surface of the photoconductive drum 1030.The latent image is moved towards the developing roller 1032 by therotation of the photoconductive drum 1030. A configuration of theoptical scanning device 1010 is described below.

The toner cartridge 1036 stores toner to be supplied to the developingroller 1032.

The developing roller 1032 attaches the toner from the toner cartridgeto the latent image formed on the surface of the photoconductive drum1030 to visualize the image information. The latent image with the toner(for convenience, hereinafter referred to as a “toner image”) is movedtowards the transfer charger 1033 by the rotation of the photoconductivedrum 1030.

The feeding tray 1038 stores recording sheets 1040. The feeding roller1037 is disposed near the feeding tray 1038. The feeding roller 1037separates the recording sheets 1040 one by one from the feeding tray1038, and feeds the recording sheet 1040 to the resist roller pair 1039.The resist roller pair 1039 temporarily hold the recoding sheet 1040separated by the feeding roller 1037, and feeds the recording sheet 1040towards the gap between the photoconductive drum 1030 and the transfercharger 1033 in synchronization with the rotation of the photoconductivedrum 1030.

In this case, a voltage having a polarity opposite to that of the toneris applied to the transfer charger 1033 to electrically attract thetoner on the surface of the photoconductive drum 1030 to the recordingsheet 1040. Due to this voltage, the toner image on the surface of thephotoconductive drum 1030 is transferred to the recording sheet 1040.Then, the transferred recording sheet 1040 is fed towards the fixingroller 1041.

The fixing roller 1041 applies both heat and pressure to the recordingsheet 1040 to fix the toner to the recording sheet 1040. The fixedrecording sheet 1040 is fed to the discharge tray 1043 by the dischargeroller 1042 to be sequentially stacked on the discharge tray 1043.

The neutralization unit 1034 removes electric charges from the surfaceof the photoconductive drum 1030.

The cleaning unit 1035 removes the toner remaining on the surface of thephotoconductive drum 1030 (residual toner). The surface of thephotoconductive drum 1030 from which the residual toner has been removedis returned to the position facing the charger 1031 again.

Next, a configuration of the optical scanning device 1010 is described.

As exemplarily shown in FIG. 2, the optical scanning device 1010 mayinclude a deflector-side scanning lens 11 a, an image-surface-sidescanning lens 11 b, a polygon mirror 13, a light source 14, a couplinglens 15, an aperture plate 16, a cylindrical lens 17, a reflectionmirror 18, a scanning control device (not shown) and the like. Thoseelements are fixed in their predetermined positions in a housing 30.

In the following, for convenience, a direction corresponding to the mainscanning direction is simplified as “main-scanning correspondingdirection”, and a direction corresponding to the sub scanning directionis simplified as “sub-scanning corresponding direction”.

The coupling lens 15 makes parallel a light flux output from the lightsource 14 to form a substantially parallel light flux.

The aperture plate 16 has an aperture part defining the beam diameter ofthe light flux having passed through the coupling lens 15.

The cylindrical lens 17 forms an image of the light flux near adeflection reflection surface of the polygon mirror 13 with respect tothe sub-scanning corresponding direction via the reflection mirror 18,the light flux having passed through the aperture part of the apertureplate 16.

The optical system disposed in an optical path between the light source14 and the polygon mirror 13 may also be called a pre-deflector opticalsystem. In this embodiment, the pre-deflector optical system includesthe coupling lens 15, the aperture plate 16, the cylindrical lens 17,and the reflection mirror 18.

The polygon mirror 13 may have, for example, a hexagonal mirror havingan inscribed circle having a radius 18 mm, and each mirror serves as adeflection reflection surface. The polygon mirror 13 deflects the lightflux from the reflection mirror 18 while rotating at a constant speedabout an axis parallel to the sub-scanning corresponding direction.

The deflector-side scanning lens 11 a is disposed in an optical pathdeflected by the polygon mirror 13.

The image-surface-side scanning lens 11 b is disposed on an opticalpath(s) having passed through the deflector-side scanning lens 11 a. Thelight flux having passed through the image-surface-side scanning lens 11b is irradiated onto the surface of the photoconductive drum 1030 sothat a light spot is formed on the surface. The light spot moves in thelongitudinal direction of the photoconductive drum 1030 by the rotationof the polygon mirror 13. Namely, the light spot scans thephotoconductive drum 1030. In this case, the moving direction of thelight spot is the “main scanning direction”; and the rotating directionof the photoconductive drum 1030 is the “sub scanning direction”.

On the other hand, an optical system disposed in an optical path betweenthe polygon mirror 13 and the photoconductive drum 1030 may also becalled a scanning optical system. In this embodiment, the scanningoptical system includes the deflector-side scanning lens 11 a and theimage-surface-side scanning lens 11 b. However, the present invention isnot limited to this configuration. For example, one or more foldingmirrors may be disposed in an optical path between the deflector-sidescanning lens 11 a and the image-surface-side scanning lens 11 b or inan optical path between the image-surface-side scanning lens 11 b andthe photoconductive drum 1030.

For example, the light source 14 includes such a surface emitting laser100 as shown in FIG. 3. In the present specification, it is assumed thatthe laser oscillation direction is the Z axis direction and twodirections orthogonal to each other on a plane surface orthogonal to theZ axis are the X axis and the Y axis. Further, FIG. 3 is across-sectional view of the surface emitting laser 100 along a surfaceparallel to the XZ plane.

The oscillation wavelength of the surface emitting laser is 780 nm band.Further, as shown in FIG. 3, the surface emitting laser 100 includes asubstrate 101, a lower semiconductor DBR 103, a lower spacer layer 104,an active layer 105, an upper spacer layer 106, an upper semiconductorDBR 107 and the like.

The substrate 101 is a n-GaAs single crystal substrate having amirror-polished surface. Further, as shown in FIG. 4(A), the normal linedirection of the mirror-polished surface (main surface) is inclined 15degrees (θ=15 degrees) towards A direction of crystal orientation [1 11] with respect to the direction of crystal orientation [1 0 0]. Namely,the substrate 101 is so-called a tilted substrate. As shown in FIG.4(B), the substrate 101 is disposed in a manner such that the directionof crystal orientation [0 −1 1] is +X direction and the direction ofcrystal orientation [0 1 −1] is −X direction.

Referring back to FIG. 3, the lower semiconductor DBR 103 is laminatedon the +Z side surface of the substrate 101 via a buffer layer (notshown). Further, the lower semiconductor DBR 103 includes 37.5 pairs ofa low refractive index layer formed of n-Al_(0.9)Ga_(0.1)As and a highrefractive index layer formed of n-Al_(0.3)Ga_(0.7)As. Further, betweenadjacent refractive index layers, to reduce electric resistance, thereis provided a composition-graded layer having a thickness of 20 nm inwhich composition is gradually changed from one composition to the othercomposition. Further, the refractive index layers are formed in a mannersuch that the optical thickness of one refractive index layer and ½(half) of the two adjoining composition-graded layers is equal to λ/4,where the symbol A denotes the oscillation wavelength. When the opticalthickness is equal to λ/4, the practical thickness (D) of the layer isgiven as D=λ/4n, where a symbol n denotes the refractive index of themedium of the layer.

The lower spacer layer 104 is laminated on the +Z side of the lowersemiconductor DBR 103, and formed of non-doped Al_(0.6)Ga_(0.4)As.

The active layer 105 is laminated on the +Z side of the lower spacerlayer 104, and may have, for example, a triple quantum well structurehaving three quantum well layers 105 a and four barrier layers 105 b asshown in FIG. 5. The quantum well layers 105 a are formed ofAl_(0.12)Ga_(0. 88)As, and the barrier layers 105 b are formed ofAl_(0.3)Ga_(0.7)As.

The upper spacer layer 106 is laminated on the +Z side of the activelayer 105, and formed of non-doped Al_(0.6)Ga_(0.4)As. A part includingthe lower spacer layer 104, the active layer 105, and the upper spacerlayer 106 may also be called a resonator structure, and is formed in amanner such that the optical thickness of the resonator structure and ½(half) of the two adjoining composition-graded layers is equal to onewavelength. Further, the active layer 105 is disposed at the middle ofthe resonator structure where a loop of an electric field standing waveis to be formed so as to obtain higher induced emission probability.

Referring back to FIG. 3, the upper semiconductor DBR 107 is laminatedon the +Z side of the upper spacer layer 106, and includes 24 pairs of alow refractive index layer formed of p-Al_(0.9)Ga_(0.1)As and a highrefractive index layer formed of p-Al_(0.3)Ga_(0.7)As.

Further, between adjacent refractive index layers in the uppersemiconductor DBR 107, to reduce electric resistance, there is provideda composition-graded layer in which composition is gradually changedfrom one composition to the other composition. Further, the refractiveindex layers are formed in a manner such that the optical thickness ofone refractive index layer and ½ (half) of the two adjoiningcomposition-graded layers is equal to λ/4.

Further, in the upper semiconductor DBR 107, a selectively-oxidizedlayer 108 formed of p-AlAs is provided (formed) in a manner such thatthe selectively-oxidized layer 108 is separated from the resonatorstructure by an optical length of λ/4. However, in FIG. 3, forconvenience, the selectively-oxidized layer 108 is provided (depicted)between the upper semiconductor DBR 107 and the resonator structure.

Further, on the +Z side of the upper semiconductor DBR 107, a contactlayer (not shown) formed of p-GaAs is provided (formed).

In the following, for convenience, the structure in which the pluralsemiconductor layers are laminated on the substrate 101 may also becalled a “laminated body”.

Next, a method of manufacturing the surface emitting laser 100 isdescribed.

(1): The above laminated body is formed by crystal growth by the MOCVD(Metal Organic Chemical Vapor Deposition) method or the MBE (MolecularBeam Epitaxy) method (see FIG. 6(A)).

In this case, trimethyl aluminium (TMA), trimethyl gallium (TMG), andtrimethyl indium (TMI) are used as group III materials, and phosphine(PH₃) and arsine (AsH₃) are used as group V materials. Further, Carbontetrabromide (CBr₄) and dimethylzinc (DMZn) are used as p-type dopantmaterials, and hydrogen selenide (H₂Se) is used as an n-type dopantmaterial.

(2): An optically transparent dielectric layer 111 a of P-SiN (SiN_(x))is formed by using the P-CVD method (plasma CVD method) (see FIG. 6(B)).In this case, the optical thickness of the dielectric layer 111 a is setto be equal to λ/4. More specifically, the refractive index n of SiN is1.83 and the oscillation wavelength λ is 780 nm; therefore, thepractical film thickness (λ/4n) of the dielectric layer 111 a is set tobe 103 nm.

(3): A first resist is applied to the surface of the dielectric layer111 a, so that resist patterns 120 a, 120 b, and 120 c are formed. Theresist pattern 120 a is formed to define an outer perimeter of a mesastructure; the resist patterns 120 b are formed to mask the region wherethe reflection rate is to be low in an emitting region; and the resistpattern 120 c is formed to mask the region where an electrode pad is tobe formed (see FIG. 6(C).

In this case, the resist patterns 120 a and 120 b are formed at the sametime. Due to this feature, a displacement of relative positionalrelationship between the resist pattern 120 a and the resist patterns120 b does not occur.

As shown in FIG. 7, the resist pattern 120 a has a square shaped outerperimeter having one side of length L4, and is a closed pattern having awidth L5. Further, as shown in FIG. 7, each of the resist patterns 120 bhas a rectangular shape having a width in X axis direction of L2 and alength in Y axis direction of L3. Those resist patterns 120 b areseparated from each other by distance L1 in the X axis direction. Inthis case, it is assumed that L1=5 μm, L2=2 μm, L3=8 μm, L4=20 μm, andL5=2 μm.

Further, the centroid of the two resist patterns 120 b is displaced fromthe center of the resist pattern 120 a to the +Y side by distance L10.In this embodiment, the substrate 101 is a tilted substrate (see FIGS.4(A) and 4(B)). Because of this feature, the crystal orientationsorthogonal to four respective side walls of the mesa structure are to bedifferent from each other (see FIG. 7). Because of the difference of thecrystal orientations, oxidation rates may be more likely to differ amongthe side walls in an oxidation process. As a result of this feature, thecenter of a current confined structure in which the oxide surrounds acurrent passage region may be displaced from the center of the mesastructure.

In this embodiment, the oxidation rates differ in order of: thedirection inclined from the [0 1 1] direction to the [1 1 1] A directionby 15 degrees >[0 1 −1] direction=[0 −1 1] direction>the directioninclined from the [0 1 −1] direction to the [1 1 1] A direction by 15degrees.

Because of the differences in the oxidation rates, the center of thecurrent confined structure is displaced from the center of the mesastructure by approximately 0.6 μm in the direction inclined from the [0−1 −1] direction to the [1 1 1] A direction by 15 degrees.

To compensate for the displacement, by previously displacing thecentroid of the two resist patterns 120 b from the center of the resistpattern 120 a to the +Y side by distance L10 (0.6 μm in this case), itmay become possible that the center of the current confined structureafter the oxidization process substantially corresponds to the positionof the centroid of the two resist patterns 120 b.

Further, a surface orientation dependency of the oxidation rate maydepend on oxidation conditions; therefore, it should be noted that thedisplacement amount and the displacement direction described herein arefor explanatory purposes only. Namely, the displacement amount and thedisplacement direction are not limited to the examples described herein.

In the following, the resist patterns formed as described above may alsobe collectively called a “first resist pattern”.

As the first resist, a general positive resist may be used. In thisembodiment, a resist of OFPR800-64cp (TOKYO OHKA KOGYO CO., LTD) isused. Further, when the first resist is applied, a spin coater may beused so that the film thickness of the first resist can be equal toapproximately 1.6 μm by adjusting the rotational speed of the spincoater. Then, exposure, development, and post baking (e.g. 2 minutes at120° C.) processes are sequentially performed to form the first resistpattern.

(4): The laminated body on which the first resist pattern is formed isplaced on a hot plate heated at 150° C. for five minutes. By heating inthis way, the first resist pattern is hardened. In the following, thisprocess may also be called a “hardening process”.

(5): The dielectric layer 111 a is etched by the ECR (Electron CyclotronResonance) etching method using Cl₂ gas. By this etching, a part of thedielectric layer 111 a which is not masked by the first resist patternis removed (see FIG. 8(A)).

(6): A second resist is applied to form a second resist pattern 123 tocover a region surrounded by the resist pattern 120 a (see FIG. 8(B)).As shown in FIG. 9, the resist pattern 123 is a square-shaped patternhaving a side length of L6. In this case, for example, it is assumedthat L6=18 μm and width L7=1 μm.

The same resist as the first resist is used as the second resist.Therefore, the second resist may be formed under the same conditions asthose of the first resist.

Further, as described above, the first resist pattern is hardened beforethe second resist is applied. Because of this feature, when the secondresist is applied, the first resist pattern is not dissolved in asolvent of the second resist. As a result, a two-layered resiststructure is formed. In this case, preferably, the heating temperatureto harden the first resist pattern is equal to or higher than 150° C.According to experiments, when the heating temperature was 140° C., thefirst resist started dissolving by just applying the second resist, andthe shape of the first resist pattern was deformed.

Further, when the second resist is exposed, a part of the first resistpattern which is not covered by the second resist pattern 123 is alsoexposed. However, since the first resist pattern has been hardened, thepart of the first resist pattern is not developed in the followingdeveloping process. As a result, the size of the first resist patternmay not be changed.

For example, as shown in FIG. 10, which is a cross-sectional view alongA-A line in FIG. 9, the second resist pattern 123 may be formed toprotect contact regions and the emitting region on the surface of themesa structure. In this case, it is assumed that length L6=18 μm, whichis shorter than one side of the outer perimeter of the resist pattern120 a by 2 μm. This difference of 2 μm may be regarded as a margin foralignment displacement.

(7): By the ECR etching method using Cl₂ gas, the laminated body isetched using the first resist pattern and the second resist pattern 123as etching masks to form the mesa structure (hereinafter simplified as“mesa”) having side surfaces where the selectively-oxidized layer 108 isexposed. In this case, this etching is set to bexpose the upper surfaceof the lower spacer layer 104 (see FIG. 11(A)).

The outer perimeter of the resist pattern 120 a defines the outerperimeter of the mesa. Because of this feature, the relative positionalrelationship between the outer perimeter of the mesa and the regionwhere the reflection rate is low in the emitting region may not bechanged.

(8): The etching masks are removed by immersing the etching masks intoacetone liquid, followed by an ultrasonic cleaning (see FIG. 11(B)).

(9): The laminated body is heated in water vapor. By doing this, Al(aluminum) in the selectively-oxidized layer 108 is selectively oxidizedfrom the outer peripheral portions of the mesa, so that a non-oxidizedregion 108 b surrounded by the Al oxide (oxidized layer) 108 a remainsat the center portion of the mesa (see FIG. 11(C)). Namely, so-called anoxide-confined structure is formed, capable of limiting the passage ofthe driving current of the emitting section to the center portion of themesa only. This non-oxidized region 108 b may also be called a currentpassage region (current injection region). By doing this, the currentpassage region having a square shape of length, for example, 4.5 μm maybe formed.

(10): An optically transparent dielectric layer 111 b of P-SiN (SiN_(x))is formed by using the P-CVD method (see FIG. 12(A)). In this case, theoptical thickness of the dielectric layer 111 a is set to be equal to2λ/4. More specifically, the refractive index n of SiN is 1.83 and theoscillation wavelength A is 780 nm; therefore, the practical filmthickness (2λ/4n) of the dielectric layer 111 b is set to be 206 nm.

(11): An etching mask is formed on the upper surface of the mesa to openwindows to the respective contact regions.

(12): The dielectric layer 111 b is etched by BHF to open windows to therespective contact regions.

(13): The etching masks are removed by immersing the etching masks intoacetone liquid, followed by ultrasonic cleaning (see FIG. 12(B)).

(14): A resist pattern having a square shape having a side length of 10μm is formed in a region to be formed as a light emitting section on theupper side of the mesa, and a p-side electrode material isvapor-deposited. As the p-side electrode material, a multilayer filmmade of Cr/AuZn/Au or a multilayer film made of Ti/Pt/Au is used.

(15): The electrode material vapor-deposited at the region to be formedas the light emitting section on the upper side of the mesa is liftedoff to form a p-side electrode 113 (see FIG. 12(C)). The regionsurrounded by the p-side electrode 113 is the emitting region.

(16): After polishing the rear side of the substrate 101 so that thethickness of the substrate 101 is equal to a predetermined thickness(e.g., approximately 100 μm), an n-side electrode 114 is formed (seeFIG. 12(D)). In this case, as the n-side electrode material, amultilayer film made of AuGe/Ni/Au or a multilayer film made of Ti/Pt/Auis used.

(17): An annealing process is performed so as to produce the ohmicconductivity of the p-side electrode 113 and the n-side electrode 114.By doing this, the mesa becomes the light emitting section.

(18) The laminated body is cut into chips.

FIGS. 13 and 14 are partially enlarged drawings showing the mesa in FIG.12(D). The emitting region 125 has a square shape having a side lengthof 10 μm. In this embodiment, the emitting region 115 is covered withthe transparent dielectric formed of P-SiN. This dielectric includes arelatively high reflection rate region 122 having an optical thicknessequal to 2λ/4 and relatively low reflection rate regions 121 having anoptical thickness equal to 3λ/4.

The two low reflection rate regions 121 are disposed at respective edgeportions of the emitting region 125 in the X axis direction. Further,when viewed from the Z axis direction, the displacement between thecentroid of the two low reflection rate regions 121 and the center ofthe current passage region 108 b was equal to or less than 0.1 μm.

When the light emitting angles of the plural surface emitting lasers 100having been manufactured as described above are measured, all the lightemitting angles in the X axis direction and in the Y axis direction wereequal to or less than ±0.2 degrees.

As is apparent from the above description, as a method of manufacturingthe surface emitting lasers, the method of manufacturing the surfaceemitting lasers 100 according to an embodiment of the present inventionis used.

As described above, in the surface emitting laser 100 according to anembodiment of the present invention, on the substrate 101, the resonancestructure including the lower semiconductor DBR 103 and the active layer105, upper semiconductor DBR 107 including the selectively-oxidizedlayer 108 and the like are laminated.

Further, the entire emitting region 125 is covered with the opticallytransparent dielectric formed of P-SiN; and the emitting region 125includes the relatively high reflection rate region 122 and therelatively low reflection rate regions 121.

Further, when the surface emitting lasers 100 are manufactured, theresist pattern 120 a and the resist pattern 120 b are formed at the sametime. Because of this feature, the relative positional relationshipbetween the outer perimeter of the mesa and the two low reflection rateregions 121 may be highly accurately and stably determined based on adesired relative positional relationship. Therefore, even when thesurface emitting lasers 100 are manufactured on a large scale, it maybecome possible to stably reduce the magnitude (absolute value) of thedisplacement amount between the centroid of the two low reflection rateregions 121 and the center of the current passage region 108 b to beequal to or less than 0.1 μm; and it may become possible to stablyreduce the magnitude (absolute value) of the light emitting angle in allthe directions to be equal to or less than 0.2 degrees.

In this case, in the surface emitting laser 100, when viewed from adirection orthogonal to the surface of the substrate after removing thep-side electrode 113, the outer peripheral portion on the upper surfaceof the mesa is covered with the optically transparent dielectric formedof P-SiN, and the thickness of the dielectric is the same as that of thepart where two-layer dielectric is formed (low reflection rate regions121).

Further, in the emitting region 125, the reflection rate in the outerperipheral part is relatively lower than that in the center part.Because of this feature, the higher-order transverse-mode oscillationmay be better controlled without reducing the fundamental transversemode of output light. Namely, the transverse mode of oscillation may bebetter controlled.

Further, the region of the relatively high reflection rate in the centerpart of the emitting region has a shape having anisotropy with respectto two directions orthogonal to each other, so that anisotropy isintentionally introduced with respect to a confining function in thetransverse direction of the laser light; therefore it may becomepossible to improve the stability of the polarization direction.

Further, it may become possible to control the higher-ordertransverse-mode and stabilize the polarization direction withoutreducing an area of the current passage region 108 b. Due to thisfeature, the electric resistance of the surface emitting laser may notbe increased, and the current density in the current confined region maynot be increased. As a result, the service lifetime of the device maynot be reduced.

Further, the entire emitting region is covered with dielectric. Becauseof this feature, oxidization and contamination of the emitting regionmay be controlled.

Further, the side surfaces of the mesa are covered with the dielectriclayer 111 b. Because of this feature, the destruction of the devicecaused due to moisture absorption may be prevented, and long-termreliability may be enhanced.

Further, the same resist is used as the first resist and the secondresist. Therefore, it may not be necessary to significantly change theprocesses from those in a conventional manufacturing method.

In the optical scanning device 1010 according to an embodiment of thepresent invention, the light source 14 includes surface emitting lasers100 and 100′. In this case, the magnitude (absolute value) of the lightemitting angle is equal to or less than 0.2 degrees, and a singlefundamental transverse mode laser light is obtained. Therefore, a tinycircular light spot may be easily formed at a desired position on thesurface of the photoconductive drum 1030. Further, the polarizationdirection is stable. Therefore, the shape of the light spot, the lightamount and the like are unlikely to be affected. As a result, a tinycircular light spot having high light density may be imaged (formed) ata desired position on the surface of the photoconductive drum 1030 byusing a simple optical system; therefore, highly-accurate opticalscanning may be performed there.

The laser printer 1000 according to an embodiment of the presentinvention includes the optical scanning device 1010. Therefore, ahigh-quality image may be formed.

Further, in the above embodiment, in above step (3), instead of formingthe resist pattern 120 b, a resist pattern 120 d to mask a regioncorresponding to a part where the reflection rate is high at the centerpart of the emitting region may be formed as shown in FIG. 15. In thiscase, in above step (10), the dielectric layer 111 b is formed so thatthe optical thickness of the dielectric layer 111 b is equal to eitherλ/4 or (λ/4)+(an even multiple of λ/4). FIG. 16 is an exemplary verticalcross-sectional view of a surface emitting laser manufactured in thisway (for convenience, “surface emitting laser 100′”). In thisconfiguration shown in FIG. 16, the dielectric layer 111 a is formed ofSiO₂, and the dielectric layer 111 b is formed of SiN. Further, the filmthickness of the dielectric in the center part of the emitting region isset to be equal to 2λ/4, and the film thickness of the dielectric in theouter peripheral part of the emitting region is set to be equal to λ/4.Further, the high reflection rate region 122 is formed in the centerpart of the emitting region and the low reflection rate regions 121 isformed in the outer peripheral part of the emitting region. In thissurface emitting laser 100′, the difference in reflection rate betweenthe high reflection rate region 122 and the low reflection rate regions121 is greater than that in the surface emitting laser 100. Therefore,the fundamental transverse mode output may be further increased.

Further, in the above embodiment, a case is described where thedielectric layer is formed of P-SiN. However, the present invention isnot limited to this configuration. For example, the dielectric layer maybe formed of any of SiO_(x), TiO_(x) and SiON. In any case, a similareffect may be obtained by appropriately determining the film thicknessesbased on their respective refractive index values.

Further, in the above embodiment, a case is described where the shape ofthe low reflection rate regions 121 is rectangular. However, the presentinvention is not limited to this configuration. For example, the shapeof the low reflection rate regions 121 may be a curved or angled shapeas shown in FIGS. 17(A) through 17(C).

Further, in the above embodiment, a case is described where the lowreflection rate part is separated into two parts. However, the presentinvention is not limited to this configuration. For example, a singlelow reflection rate part may be formed as shown in FIGS. 17(D) through17(G).

Further, as shown in FIGS. 18(A) through 18(C), the low refraction ratepart 121 may be formed in the center part of the emitting region and thehigh reflection rate region 122 may be formed in the outer peripheralpart of the emitting region, so that higher-order mode can beselectively operated.

Further, in the above embodiment, a case is described where the positiveresist is used as the first resist and the second resist as well.However, the present invention is not limited to this configuration. Forexample, a negative resist such as OMR85-45cp (TOKYO OHKA KOGYO CO.,LTD) may be used as the first resist, and a positive resist such asOFPR800-64cp (TOKYO OHKA KOGYO CO., LTD) may be used as the secondresist. Even in this case, the relative positional relationship betweenthe outer perimeter of the mesa and the two low reflection rate regions121 may be highly accurately and stably determined in accordance with adesired relative positional relationship.

In this case, the solvents differ depending on the resists. Therefore,after the first resist pattern has been formed, even when the secondresist is applied, the first resist pattern may not be dissolved.Therefore, the hardening process may not be necessarily performed on thefirst resist pattern.

Further, in this case, even when a part of the first resist patternwhich is not covered by the second resist pattern 123 is exposed, thecomposition of the part of the first resist pattern may be changed to behardened. Therefore, the size of the of the first resist pattern may notbe changed. Needless to say, different developing fluids are useddepending on the resist patterns. Therefore, when the second resistpattern is being developed, the first resist pattern may not bedeveloped; therefore, the size of the first resist pattern may not bechanged.

Further, in this case, even when it may be required to form the secondresist pattern again by a rework process due to alignment displacementor an error, the size of the first pattern may not be changed becausedifferent resists are used. For example, in a process where the secondresist pattern is formed again by rework process, after the entiresurface is exposed to expose the second resist, the second resist isremoved by developing using a developing fluid for the second resist.Even in this case, the first resist pattern may have a resistance to thedeveloping fluid for the second resist, so that the size of the firstresist pattern may not be changed.

On the other hand, when the hardening process is performed on the firstresist pattern, a vertical cross-sectional shape of the first resistpattern may be changed into a round shape (see FIG. 19). In a dryetching process, it is known that a tilting angle of the etched sidewall is determined depending on an etching selection ratio between theresist and the to-be-etched material. A reason of this change is thatnot only the to-be-etched material but also the resist may be etched. Asa result, the resist pattern is slimmed and the side wall of theto-be-etched material is tilted depending on a result of the slimmedpattern. This tilt determines the vertical cross-sectional shape. Whenthe vertical cross-sectional shape is changed into a round shape, theangle of the etched side wall may vary, which may cause a stepdisconnection of an electrode wiring.

To resolve this problem, before the hardening process is performed onthe first resist pattern, an ultraviolent light (UV-light) may beirradiated onto the laminated body while the laminated body is heated.By doing this way, the surface of the first resist pattern may behardened, and as a result, deforming the vertical cross-sectional shapeinto the round shape in the hardening process may be prevented.

Practically, for example, the irradiation of the UV-light may beperformed by using the UV dry cleaner (UV-1) (Samco, Inc.). Thisapparatus is basically used to remove organic matter on the surface of asubstrate using UV-light and ozone.

However, by introducing nitrogen instead of oxygen, only the effect ofthe UV-light can be obtained. In this case, the wavelengths of theUV-light are 253.7 nm and 184.9 nm, and the power is 110 W (0.35 W/cm²because φ of the lamp is 200 mm). The laminated body is heated at 130°C. and the UV-light is irradiated for five minutes. By doing this, inthe hardening process (at 150° C. for five minutes), deforming thevertical cross-sectional shape into the round shape in the hardeningprocess may be prevented.

In the above embodiment, a case is described where the optical thicknessof the dielectric layer 111 a is λ/4. However, the present invention isnot limited to this configuration. The present invention may be appliedas long as the optical thickness of the dielectric layer 111 a is equalto an odd multiple of λ/4.

In the above embodiment, a case is described where the optical thicknessof the dielectric layer 111 b is 2λ/4 . However, the present inventionis not limited to this configuration. The present invention may beapplied as long as the optical thickness of the dielectric layer 111 bis equal to an even multiple of λ/4.

Further, in the above embodiment, the light source 14 may include, forexample, a surface emitting laser array 200 as shown in FIG. 20 insteadof using the surface emitting laser 100.

In the surface emitting laser array 200, there are providedtwo-dimensionally arranged plural (21 in this case) emitting sectionsformed on the same substrate. In this configuration of FIG. 20, the Xaxis direction corresponds to the main scanning direction, and the Yaxis direction corresponds to the sub scanning direction. The pluralemitting sections are arranged in a manner such that when all theemitting sections are orthographically projected on a virtual lineextending in the Y axis direction, the distance between the adjacentemitting sections is equal to a constant distance d2. In thisdescription, the distance between the adjacent emitting sections refersto the distance between the centers of adjacent emitting sections.Further, the number of the emitting sections is not necessarily limitedto 21.

As shown in FIG. 21, which is a cross-sectional view along A-A line ofFIG. 20, each of the emitting sections has a similar configuration tothat of the surface emitting laser 100. Further, the surface emittinglaser array 200 may be manufactured in a similar manner to that inmanufacturing the surface emitting laser 100. Therefore, in eachemitting section, when viewed from the Z axis direction, the magnitude(absolute value) of the displacement amount between the centroid of thetwo low reflection rate regions 121 and the center of the currentpassage region 108 b may be reduced to be equal to or less than 0.1 μm;and the magnitude (absolute value) of the light emitting angle in allthe directions may be reduced to be equal to or less than 0.2 degrees.Further, among the emitting sections, it may become possible to obtainplural single fundamental transverse mode laser lights having the samepolarization direction. Therefore, twenty-one tiny circular light spotshaving high light density may be simultaneously formed at respectivedesired positions on the surface of the photoconductive drum 1030.

Further, in the surface emitting laser array 200, when all the emittingsections are orthographically projected on a virtual line extending inthe Y axis direction, the distance between the adjacent emittingsections is equal to a constant distance d2. Because of thisconfiguration, by controlling the turn-on timings of the emittingsections, the configuration of the surface emitting laser array 200 maybe regarded as a configuration where the emitting sections are arrangedat regular intervals in the sub scanning direction on thephotoconductive drum 1030.

Further, for example, when the distance d2 is determined to be 2.65 μmand the magnification of the optical system is determined to be 2 times,high density writing of 4800 dpi (dots per inch) may be achieved.Obviously, for example, by increasing the number of the emittingsections in the main-scanning corresponding direction; by changing thearray layout by reducing the pitch dl in the sub-scanning correspondingdirection to further reduce the distance d2; or by reducingmagnification of the optical system, the density may be furtherenhanced, thereby enabling achieving higher quality printing. Further,the writing distance in the main scanning direction may be easilycontrolled by controlling the turn-on timings of the emitting sections.

Further, in this case, even when the writing dot density is required tobe increased, the laser printer 1000 may perform printing withoutreducing the printing speed. Further, when assuming that writing dotdensity is to be maintained, the printing speed may be furtherincreased.

Further, preferably, the width of the grooves formed between adjacentemitting sections is equal to or greater than 5 μm to ensure electricaland spatial separations between the emitting sections. When the width istoo narrow, it may become difficult to control etching in manufacturing.Further, preferably, the size (side length) of the mesa is equal to orgreater than 10 μm. When the size is too small, the heat may not beeasily discharged, which may reduce the performance.

Further, in the above embodiment, instead of using the surface emittinglaser 100, the surface emitting laser array 200 may be used, having beenmanufactured in a similar manner to that in manufacturing the surfaceemitting laser 100 and including the emitting sections arranged inone-dimensional alignment.

Further, in the above embodiment, a case is described where the normalline direction of the main surface of the substrate is inclined 15degrees. towards A direction of crystal orientation [1 1 1] with respectto the direction of crystal orientation [1 0 0]. However, the presentinvention is not limited to this situation. When a tilted substrate isused as the substrate, the present invention may be applied as long asthe normal line direction of the main surface of the substrate isinclined towards one direction of crystal orientation <1 1 1> withrespect to one direction of crystal orientation <1 0 0>.

Further, in above embodiment, a case is described where the substrate isthe tilted substrate. However, the present invention is not limited tothis configuration.

Further, in the above embodiment, a case is described where theoscillation wavelength of the emitting section is 780 nm band. However,the present invention is not limited to this configuration. Theoscillation wavelength may be changed in accordance with thecharacteristics of the photoconductive body.

Further, the surface emitting laser 100 and the surface emitting laserarray 200 may also be used in applications other than an image formingapparatus. In such a case, the oscillation wavelength may be, forexample, 650 nm band, 850 nm band, 980 nm band, 1.3 μm band, 1.5 μm bandor the like. Further, in this case, as the semiconductor material usedfor the active layer, an appropriate mixed crystal semiconductormaterial in accordance with the oscillation wavelength may be used. Forexample, an AlGaInP-based mixed crystal semiconductor material may beused in 650 nm band; an InGaAs-based mixed crystal semiconductormaterial may be used in 980 nm band; and a GaInNAs(Sb)-based mixedcrystal semiconductor material may be used in 1.3 μm band and 1.5 μmband.

Further, by appropriately selecting the material and the configurationof the reflection mirrors in accordance with the oscillation wavelengthto be used, it may become possible to form the emitting section inaccordance with any oscillation wavelength. For example, as the mixedcrystal other than AlGaAs mixed crystal, AlGaInP mixed crystal or thelike may be used. Further, preferably, the low reflection rate region(layer) and the high reflection rate region (layer) may be formed byusing materials that are transparent to the oscillation wavelength andthat have different reflection rates from each other as much aspossible.

In the above embodiment, the laser printer 1000 is described as an imageforming apparatus. However, the present invention is not limited to thisconfiguration.

For example, the present invention may also be applied to an imageforming apparatus capable of irradiating a laser light onto a medium(such as a sheet) which is capable of forming a color by the laserlight.

Further, for example, the present invention may also be applied to animage forming apparatus using a silver-salt film as an image carrier. Inthis case, a latent image is formed on the silver-salt film by opticalscanning, and the latent image may be visualized by a process similar toa developing process performed in a typical silver salt photographicprocess. Then, the image may be transferred to a printing paper byperforming a process similar to the printing process in the typicalsilver salt photographic process. Such an image forming apparatus mayinclude an optical photoengraving apparatus and an optical drawingapparatus capable of drawing a CT scan image and the like.

Such an image forming apparatus may further include a color printer 2000having plural photoconductive drums as shown in FIG. 22.

The color printer 2000 is a tandem-type multi-color printer forming afull-color image by combining four colors (black, cyan, magenta, andyellow). The color printer 2000 includes a station for black (K) (havinga photoconductive drum K1, a charger K2, a developing device K4, acleaning unit K5, and a transfer device K6), a station for cyan (C)(having a photoconductive drum C1, a charger C2, a developing device C4,a cleaning unit C5, and a transfer device C6), a station for magenta (M)(having a photoconductive drum Ml, a charger M2, a developing device M4,a cleaning unit M5, and a transfer device M6), a station for yellow (Y)(having a photoconductive drum Y1, a charger Y2, a developing device Y4,a cleaning unit Y5, and a transfer device Y6), and an optical scanningdevice 2010, a transfer belt 2080, a fixing unit 2030 and the like.

The photoconductive drums rotate in the respective arrow directionsshown in FIG. 22. In the vicinity of each photoconductive drum, alongthe rotating direction, there are disposed in order of: the charger, thedeveloping device, the transfer device, and the cleaning unit. Thechargers uniformly charge the surface of the respective photoconductivedrums. The optical scanning device 2010 irradiates light onto thesurfaces of the photoconductive drums to form latent images on therespective photoconductive drums, the surfaces having been charged bythe respective chargers. Then, colored toner images are formed on thesurfaces of the photoconductive drums by the respective developingdevices. Further, the colored toner images are superposed onto therecording paper on the transfer belt 2080 by the respective transferdevices. Finally, the superposed colored image is fixed to the recordingpaper by the fixing unit 2030.

The optical scanning device 2010 includes light sources having either asurface emitting laser or a surface emitting laser array manufactured bya method similar to that of the surface emitting laser 100. Because ofthis feature, the optical scanning device 2010 may achieve the sameeffect as that achieved by the optical scanning device 1010. Further,the color printer 2000 includes the optical scanning device 2010;therefore, the color printer may achieve the same effect as thatachieved by the laser printer 1000.

Further, in the color printer 2000, a color displacement may occur dueto manufacturing error or positional error of used parts or the like.Even in such a case, when the light sources of the optical scanningdevice 2010 have the surface emitting laser array similar to the surfaceemitting laser array 200, the color displacement may be bettercontroller by selecting the emitting section to be turned ON.

INDUSTRIAL APPLICABILITY

As described above, a method of manufacturing a surface emitting laseraccording to an embodiment of the present invention may be appropriateto stably manufacturing a surface emitting laser having the magnitude(absolute value) of displacement amount equal to or less than 0.1 μmwhile better controlling the transverse-mode oscillation. Further, in asurface emitting laser and a surface emitting laser array according toan embodiment of the present invention, it may be adequate to reduce themagnitude (absolute value) of the light emitting angle to be equal to orless than 0.2 degrees while better controlling the transverse-modeoscillation without incurring high cost.

Further, an image forming apparatus according to an embodiment of thepresent invention may be appropriate to forming a high-quality imagewithout incurring high cost.

The present application is based on and claims the benefit of priorityof Japanese Patent Application Nos. 2009-128434 filed on May 28, 2009and 2010-009820 filed on Jan. 20, 2010, the entire contents of which arehereby incorporated herein by reference.

1. A method of manufacturing a surface emitting laser, the surfaceemitting laser including: a laminated body in which a lower reflectionmirror, a resonance structure, and an upper reflection mirror arelaminated on a substrate, the resonance structure including an activelayer, the upper reflection mirror including a selectively-oxidizedlayer, and a mesa structure formed in the laminated body and providingan emitting section, the emitting section including a current confinedstructure and an emitting region, the current confined structureincluding an oxide surrounding a current passage region, the emittingregion including a relatively high reflection rate part and a relativelylow reflection rate part, the method comprising: a first dielectriclayer laminating step of laminating a first transparent dielectric layeron an upper surface of the laminated body; a first resist patternforming step of forming a first resist pattern on an upper surface ofthe first transparent dielectric layer, the first resist patternincluding a pattern configured to define an outer perimeter of the mesastructure and a pattern configured to protect a region corresponding toone of the relatively high reflection rate part and the relatively lowreflection rate part included in the emitting region; a dielectric layeretching step of etching the first transparent dielectric layer by usingthe first resist pattern as an etching mask; and a second resist patternforming step of forming a second resist pattern configured to protect aregion corresponding to all of the emitting region, wherein the firstdielectric layer laminating step, the first resist pattern forming step,the dielectric layer etching step, and the second resist pattern formingstep are performed before the mesa structure is formed.
 2. The method ofmanufacturing a surface emitting laser according to claim 1, furthercomprising: a second dielectric layer laminating step of, after thecurrent confined structure is formed, laminating a second transparentdielectric layer on an upper surface of the laminated body, the secondtransparent dielectric layer having an optical thickness of either aneven multiple of (oscillation wavelength/4) or (oscillationwavelength/4)+(an even multiple of (oscillation wavelength/4)), whereinin the first dielectric layer laminating step, the first transparentdielectric layer having an optical thickness of an odd multiple of(oscillation wavelength/4) is laminated.
 3. The method of manufacturinga surface emitting laser according to claim 1, wherein the substrate isa tilted substrate, in the first resist pattern forming step, a centroidof the pattern configured to protect the region corresponding to one ofthe relatively high reflection rate part and the relatively lowreflection rate part included in the emitting region is displaced from acenter of the pattern configured to define the outer perimeter of themesa structure in response to a positional displacement of the currentpassage region.
 4. The method of manufacturing a surface emitting laseraccording to claim 1, wherein the first resist pattern and the secondresist pattern are formed using respective resists having a samephotosensitive characteristic.
 5. The method of manufacturing a surfaceemitting laser according to claim 4, further comprising: a first resistpattern hardening step of, before the dielectric layer etching step isperformed, hardening the first resist pattern.
 6. The method ofmanufacturing a surface emitting laser according to claim 5, furthercomprising: an irradiating step of, before the first resist patternhardening step is performed, irradiating a UV-light onto the firstresist pattern while heating the substrate.
 7. The method ofmanufacturing a surface emitting laser according to claim 1, whereinphotosensitive characteristics of a resist used to form the first resistpattern are different from those of a resist used to form the secondresist pattern.
 8. A surface emitting laser comprising: an emittingsection having a mesa structure in which a lower reflection mirror, aresonance structure, and an upper reflection mirror are laminated on asubstrate, the resonance structure including an active layer, the upperreflection mirror including a current confined structure including anoxide surrounding a current passage region, the emitting sectionincluding an emitting region, the emitting region having an entiresurface including a first surface part on which one dielectric layer isformed and a second surface part on which two dielectric layers areformed so that the emitting region includes a relatively high reflectionrate part and a relatively low reflection rate part, wherein when viewedfrom a direction orthogonal to the substrate after removing an electrodesurrounding the emitting region, an upper surface of an outer perimeterof the mesa structure is covered with dielectric, and a thickness of thedielectric covering the upper surface of the outer perimeter of the mesastructure is a same as that of the second surface part on which twodielectric layers are formed in the emitting region.
 9. A surfaceemitting laser array comprising: integrated plural of the surfaceemitting lasers according to claim
 8. 10. An optical scanning devicecapable of scanning a to-be-scanned surface with a light, the opticalscanning device comprising: a light source having a surface emittinglaser according to claim 8; a deflector configured to deflect a lightfrom the light source; and a scanning optical system configured to focusthe light deflected by the deflector onto the to-be-scanned surface. 11.An optical scanning device capable of scanning a to-be-scanned surfacewith a light, the optical scanning device comprising: a light sourcehaving a surface emitting laser array according to claim 9; a deflectorconfigured to deflect a light from the light source; and a scanningoptical system configured to focus the light deflected by the deflectoronto the to-be-scanned surface.
 12. An image forming apparatuscomprising: an image carrier; and an optical scanning device accordingto claim 10 configured to scan a light onto the image carrier, the lightbeing modulated based on image information.
 13. The image formingapparatus according to claim 12, wherein the image information ismulti-colored.